1. Field of the Invention
The present invention relates to the prevention of scale formation on metal surfaces in contact with hard-water brines. More particularly, it is concerned with preventing scale deposition in oil wells and associated equipment.
2. Description of the Prior Art
A variety of methods for inhibiting scale deposition in geologic formations and in oil or gas well equipment exposed to hard water or natural brines during the production of oil and gas have been suggested and utilized by the oil industry. Such processes and compositions have historically been the subject of many patents; for example, U.S. Pat. Nos. 3,429,824; 3,462,365; 3,487,018; 3,488,289 and 3,502,587 involve phosphate on phosphonate esters of oxyalkylated or oxyalkyl related compounds while U.S. Pat. Nos. 3,412,025; 3,477,956; 3,620,974; 3,557,001; 3,591,513; 3,597,352 and 3,617,578 involve phosphate or phosphonate esters of oxyalkylated or oxyalkyl related amine compounds. Furthermore, the problems associated with scale deposition from hard water present in oil wells and the like have historically been recognized and well documented in the patent literature; for example, see Chapter 3 of "Descaling Agents and Methods," by J. A. Szilard, copyright 1972 by Noyes Data Corporation, Park Ridge, N. J., Library of Congress Catalog Card No. 78-185161, for a patent survey with comments. In particular, French Pat. No. 2,290,505 discloses the monophosphate esters of monoethoxyl related urea compounds derived by phosphorylation of the reaction product of urea and an alkanolamine as scale inhibitors. However, scale problems continue to plague commercial oil and gas producing operations despite numerous suggested remedies.